This invention generally relates to intravascular catheters and particularly to intravascular catheter assemblies for delivering radiation treatment to a body lumen while providing blood perfusion through the body lumen past the catheter while the radiation treatment is being administered.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter having a preshaped distal tip is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral artery and is advanced therein until the preshaped distal tip is disposed within the aorta adjacent to the ostium of the desired coronary artery. The guiding catheter is then twisted and torqued from its proximal end to turn its distal tip so that it can be guided into the coronary ostium. In an over-the-wire dilatation catheter system, a guide wire and a dilatation catheter having an inflatable balloon on the distal end thereof are introduced into, and advanced through, the proximal end of the guiding catheter to the distal tip of the guiding catheter seated within the coronary ostium. The distal tip of the guide wire is usually manually shaped (i.e. curved) by the physician or one of the attendants before it and the dilatation catheter are introduced into the guiding catheter. The guide wire is usually first advanced out of the distal end of the guiding catheter and is maneuvered into the patients coronary vasculature containing the stenosis to be dilated, and is then advanced beyond the stenosis. Thereafter, the dilatation catheter is advanced over the guide wire until the dilatation balloon is position across the stenosis. Once the dilatation catheter is in positioned, the balloon of the catheter is filled with radiopaque liquid at relatively high pressures (e.g., generally about 4-12 atmospheres) to inflate it to a predetermined size (preferably the same as the inner diameter of the artery at that particular location) in order to radially compress the atherosclerotic plaque of the stenosis against the inside of the wall of the artery, thereby increasing the diameter of the occluded area. The balloon can then be deflated so that the catheter can be removed and blood flow resumed through the dilated artery.
One common problem that sometimes occurs after an angioplasty procedure has been performed is the development of restenosis at, or near, the original site of the stenosis. When restenosis occurs, a second angioplasty procedure or even bypass surgery may be required, depending upon the degree of restenosis. In order to reduce the likelihood of the development of restenosis and thereby prevent the need to perform bypass surgery or subsequent angioplasty procedures, various devices and procedures have been developed for preventing restenosis after arterial intervention. For example, an expandable cage (commonly termed "stent") designed for long term implantation with the body lumen has been utilized to help prevent the occurrence of restenosis.
More recent devices and procedures for preventing restenosis after arterial intervention employ the use of a radiation source to inhibit the proliferation of smooth muscle cells which are believed to be the primary cause of restenosis. Balloon catheters have been used to deliver and maintain the radiation source in the area where arterial intervention has taken place, exposing the area to a sufficient radiation dose to abate cell growth. Two such devices and methods are described in U.S. Pat. No. 5,302,168 (Hess) and U.S. Pat. No. 5,503,613 (Weinberger). Other devices and methods which utilize radiation treatment delivered by an intravascular catheter are disclosed in commonly-owned and assigned co-pending application U.S. Ser. No. 08/654,698, filed May 29, 1996, entitled Radiation-Emitting Flow-Through Temporary Stent and co-pending application Ser. No. 08/705,945, filed Aug. 29, 1996 now U.S. Pat. No. 5,782,740, entitled Radiation Dose Delivery Catheter with Reinforcing Mandrel, which are incorporated herein by reference. Another medical device for the treatment of a body vessel by radiation is disclosed in European Patent App. 0 688 580 A1 (Schneider).
One problem common to many of the balloon catheters which provide radiation treatment to a particular part of a patient's vascular system is that it is sometimes preferable to treat the target area with a lower dose rate, delivering the desired therapeutic dose over a longer period of time, rather than a higher dose rate over a shorter period of time. If conventional balloon catheters are utilized to center the radiation source in the artery, then the inflated balloon will inhibit or restrict the flow of blood through the artery, which can pose serious risk of damage to tissue downstream from the occluded portion of the artery since the tissue will be deprived of oxygenated blood. As a result, the time in which the balloon can remain expanded within the artery would be diminished, effecting the time period in which the radiation dosage can be maintained in the area of the artery where restenosis may occur. Thus, a higher radiation dose rate may have to be used due to the occlusion of the vessel caused by the inflated balloon catheter, which again, may not be as advantageous as providing a lower dose rate.
What has been needed and heretofore generally unavailable in catheters which provide treatment of the body vessel with a radiation source is an intravascular catheter assembly which allows delivery of a radiation source to the area where restenosis may occur for a period of time sufficient to kill the cells and prevent development of restenosis while allowing blood to perfuse pass the occluded region during the radiation procedure. Such an intravascular catheter should be flexible so that it can be expanded on a curved portion of a body lumen, such as a coronary artery, while properly centering and maintaining the radiation source wire within the body lumen. Additionally, such an intravascular catheter would have to be relatively easy and inexpensive to manufacture, have an expandable region that is strong and reliable under pressure, and capable of being formed in a variety of shapes to allow flexibility in the amount and pattern of expansion and deformation of the expandable region. The present invention satisfies these and other needs as will be described hereinafter.